My PC turns on and off on by itself

[SnowPaleVampire]

My computer turns on and off with no reason, I have already replaced the psu, it worked for a while then and the problem started again ! I have checked the plug and everything a hundred times and it's still not working.
I was wondering if something was wrong with the electricity in the house? Also would the UPS help ?

 

[LookinAround]

I'd start by turning off power management options and confirm the auto on/off problems don't occur

1) In Device Manager, rt click Properties for EACH of your network adapters. Click the power management tab. UNCHECK "Allow computer to turn this device off to save power" - which btw will also prevent it from waking up from standby mode

2) In Control Panel->Power Options, disable and settings allowing for sleep/standby or hibernation modes